Structure Determinations of Conformations by NMR

美国国家科学基金会化学部的有机和大分子化学项目支持加州理工学院的约翰·d·罗伯茨教授，他将利用并扩展琥珀酸的强氢键单离子的初步成功，通过核磁共振实验确定其他1,2 -二取代乙烷在液晶或溶性溶液中取向的构象的旋转二面角的非常重要的值。第二个目标是进一步了解溶剂对间扭式和反式（反）构象之间平衡位置的影响，特别是那些携带极性、电离和潜在氢键取代基的构象，这些取代基除了具有重大的化学意义和重要性外，在涉及生命系统的分子中无处不在。这项工作将扩展到电子、氢键和溶剂效应将与预期的大量立体效应相对抗的化合物，后者通常被认为是构象偏好的主要原因，尽管大量经验表明，立体效应基本上不存在或对构象偏好的影响相对较小，除非X和Y取代基都是四面体基团，如叔丁基、三甲基铵、磺酸之类的。该研究将对二取代乙烷的构象性质和相关能量学的实验验证提供深入的了解。取代乙烷中二面角与能量的关系对于进一步理解静电和空间对自由能的贡献具有直接意义，不仅影响有机化学，而且与遥远的领域相关，例如理解蛋白质侧链结构和动力学。拟议的活动预计会产生几个更广泛的影响，特别是通过将研究和教学结合起来，为大学本科生和积极的高中生带来好处。其中一些是加州理工学院的学生，其他来自全国各地，或来自国外，其中一半以上是女性。一个项目已经到位，让他们接触到一个年轻新教员经历的缩影。首先要写一份研究计划，然后由知识渊博的教师小组审核。有了成功，计划如何开始研究工作；学习新的合成技术或涉及复杂的仪器；撰写研究结果供发表；在公开会议上以专业化学小组使用的方式做口头报告或海报。在20年的时间里，110名本科生参与了这项研究，发表了25篇论文，还有几篇基本上是最终稿。该提案列出了9篇以本科生和高中生为共同作者的文章的标题和30个以学生为共同作者的项目标题。这些项目在2003-2007年期间进行。

The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports Professor John D. Roberts at the California Institute of Technology, who will capitalize on and extend an initial success with the strongly hydrogen-bonded monoanion of succinic acid for determining experimentally by NMR, the very important values of rotational dihedral angles of conformers of other 1, 2-disubstituted ethanes oriented in liquid-crystal or lyotropic solutions. A second objective is to contribute further to understanding the influences of solvents on the positions of equilibria between gauche and trans (anti) conformations, especially ones carrying polar, ionized and potentially hydrogen-bonded substituent groups that, besides being of substantial chemical interest and importance, are ubiquitous in molecules involved in living systems. This effort will be extended to compounds where electronic, hydrogen bonding and solvent effects are to be pitted against expected substantial steric effects, the latter commonly regarded as the primary cause of conformational preferences, even though much experience, shows that steric effects are essentially nonexistent or relatively minor in their influence on conformational preferences, unless the X and Y substituents are both tetrahedral groups, such as tert-butyl, trimethylammonium, sulfonic acid and the like. The research will provide an in-depth understanding of the conformational properties of disubstituted ethanes and experimental validation of the associated energetics. The dihedral angle versus energy relation in substituted ethanes is of direct relevance for developing improved understanding of both electrostatic and steric contributions to the free energy, impacting not only organic chemistry but also being relevant to far removed areas, such as understanding protein side chain structure and dynamics.Broader impacts expected to result from the proposed activities are several, but especially through integrating research and teaching for the benefit of university undergraduates and motivated high-school students. Some are Caltech students, others come country-wide, or from abroad, more than half are women. A program is in place to expose them to a microcosm of the experience of a new young faculty member. It starts with writing a research proposal, then having it reviewed by a knowledgeable faculty group. With success there, planning on how to get the research work started; learning new techniques in synthesis or involving sophisticated instrumentation; writing up the results for publication; and presenting a oral report or poster at a public meeting in the style used by professional chemistry groups. Over a period of 20 years, 110 undergraduates have participated with 25 papers published and several others in essentially final draft form. The proposal lists the titles of nine articles with the names of undergraduates and high school students as co-authors and thirty project titles listing the students' names. These projects were carried out during 2003-2007.